Spare plug



L. KEBLER.

SPARK PLUG.

APPLlcArloN FILED ocT.1s. lsu.

Patented Jan. 17, 1922.

INVENTOR ,4 UUR/VE Y UNITED STATES PATENT OFFICE.

LEONARD KEBLER, OF BRONXVILLE, NEW YORK, ASSIGNOR T0 WARD LEONARD ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SPARK PLUG.

Specification of Letters Patent.

Patented Jan. 1'7, 1922.

To all whom it may concern.'

Be it known that I,LE0NARD Kinsman, a. citizen of the United States, residing at Bronxville, in the county of Westchester and State of New York, have invented certain new and useful Improvements in Spark Plugs, of which the following is a specication.

The principal object of my invention is to provide a new and improved spark plug for use with gas engines. Other objects of my invention relate to providing a spark plug that shall be non-leaking under` high compression, that shall maintain its integrity under any extremes of temperature and under sudden changes of temperature to which it may be subjected in practice,

that shall be effectively insulated for allv shall otherwise be temperatures of use, and eiicient and durable. All these and other objects of my invention will be more readily.. appreciated in connection with the follow' ing specification and claims taken with the accompanying drawings.

Ordinary automobile engines are operated at a compression much, if any, more than pounds'per square inch, but the modern aeroplaneen-4 gine is operated at a much hi her compression, namely, about 125 poun s.

panying higher temperatures and abrupt and extreme temperature changes, serious troubles are encountered if the ordinary spark plugs such as used with automobileengines are ern loyed. The porcelainsleeve ordinarily use inautomobile has a coeliicient of heat expansion per egree centigrade between 0.0000030 and 0.0000060, whereas sion of iron is about 0.0000120. Hence, even though the parts may be initially assembled tight y, they are likely to get loose and permit leakage at the extremely high temperatures at which aeroplane engines are operated. In my improved plug such leakage is impossible, because in my plugthe shell and insulator are sealed with an enamel which is most intimately united to the iron and to the insulator, thus completely seal ing thc plug against leakage. This enamel is selected and prepared to have an elastic range sulicicntv for any dilierential expansion between the insulator and the iron.

The electrical resistivity of porcelain,

l electrode (before ignition) of not- With this' much higher compression and the accom-` spark pluors the coeliicient of expan-V glass, and substances of that character usually falls oil very decidedly with increasing temperatures, so that in an ordinary spark plug with a porcelain bushing between the and the iron shell, ii' the hot cylinder gases come in contact therewith, then the electric current impulses will leak right throl'igh the porcelain between the electrode and e shell when such a plug is attempted to be operated at the high temperature encountered in aeroplane practice. Illustrating the failure in resistivity at higher temperatures, Iwill mention that for temperatures centigrade and for resistivity expressed in megohms, ordinary soda lime glass is 500,000-at 18 and is only 100 at 145; Jena tubing is 200,000,000 at 18, 30,000,000 at 115, 18,000,000 at 150 and 0.01 at 7 50.

Mica isa very superior insulator and preserves this quality at high temperatures and therefore I also provide mica insulation to preventi any leaka e of current, where the heatvv is intense. owever, mica disintegrates,v when exposed directly to the hot engine gases and. it must be carefully protected from them. I

The parts of a spark plug with which the hot engine gases come in contact are liable to be subjected to abrupt and extreme temerature changes, as `vvhenafter driving at l. speed, the :engine is shut oli. and an: is drawn through the cylinders.. Under these circumstances, such, a memberiasA-a thick piece of porcelain would', crack on its-face because, having a considerable coeiicient oi heatexpansion as already mentioned, the surface would contract and crack before the interior portion could contract. As a protective barrier. I employ a comparatively thin shell, so that its temperature condition will change more nearly at once throughout and it will not besubjected to extreme strains on account of differential heating and cooling. A satisfactory material for this-shell is porcelain, glass, or fused silica, or lava, or similar material. By having the shell member thin-walled, any dangerous differential expansion of its parts is avoided, as heretofore explained.

'Ihe coefficient of heat expansion of fused silica is very low, namely, only about 0.0000006, and this is an important quality to give permanence with respect to sudden temperature changes, because it reduces the around the ho e.

degree of differential expansion and contraction. 4 As is well known, fused silica is also highly refractory td heatand addition it has a high resistivity which it preserves in high degree when its temperature is raiseda,

With the same units as above, it is over 200,000,000 ai; 18 iq 150, 2,500,000an12509, 30,000 at 350, and 30 at 700". Thus, it W1ll be seen that fused silica is a satisfactory material for the barrier. It is difficult to obtain fused silica in massive' shapes, Such for example as the porcelain members of ordinary automobile spark plugs, butlit'is commonly found in chemical laboratories drawn out in tubes or inthe formof crucibles or evaporating dishes. I sometimes employ a simple shape of-fusedisilica` Wlilelris eas-y tomalre. A

Byrmaking the it" r'unctions'as a relieves the mica surrounding itj becoming oyerheated;

plug electrode of lai-ges'ize,

In: thedraw "gs Iv4 have illustrate'd'two-;

which my invention-may be embodied, but it Wilt-'bez understood' that.

' v. ity of; gasftightnessiwhen specific forms'in these arev by Way of example'andith'at r'ny invention com prehe'ndls` other`4 modifications; Proceeding non7 yto a specific description of the forms shown in the draWingS, f

cationand Fig.A 2 show-vs.; asimilar 'viebiir fof another-'modification threade compre'ible 'or deformable materiahi VIliis otherwis'breal'r the teu '13f." 4h1 li`elarge ''opper electrode- '15 eitends'f :through a central hole in th'ebottom ofi the `sliell 13, tleflave l'butt-in'g a ainst nal 17 vis securely 15; Thin sheets of mica'are wrappedround and round the electrode 15y 2111118: l"Thevine" sulator 27 is then putin place. parts are assembled to` the vextent hereto; foredesribed, the shell'A 1l and'tlie insulatorJ 27 Vare cemented together with a, fused vittel ons enamel' 19 havingy(Wheifc'o'oled)` approximately Ithe sarnecoeliicient of heat expansion asthe iron, or having an elastic range whichV allowsthe enamel to adhere to the shell 11 and' to the insulator@ 27 inspite of anydill'erence in expansion'when heated. This is accomplished by heating the previously asgemhlcd 'parts tol proper temperature,V aclear red heat, and then introducing' the. enamel in'powdered or granular form and continuinf;f the heating until the enamel is fused. The electrode 15 and theV insulator 27 are then cemented in the same Way at 20. Then the parts are cooled and the enamel sets` trod 15 218 by wrapping the mica sheets conductory of heat; and so the beam-gef Eaie- Sii-1' 'The nickel electrode ter'ni-r f' engaged iniftlie" electrode;

After thel tightly engaging the interior Wall of the shell l1 at 25 and around the insulator 27 at"24i and also likewise engaging the elecand'the insulator-"27. Thereafter 22, and 23 are mounted on the screw the nuts portion 21 of the electrode 15 so threaded jthat a vconductor can be engaged thereto.

The terminal 26 of nickel is secured in a hole inthe` lower edgeof the plug shell l1.

I prefer to form the insulating member around cylindcally; instead-of building up washers; because for example, if the member 18 is= constructed in 'the latter manner, any trace of iron in one washer gives a radial path-of comparatively low resistance throughV member; Whereas by my' manner of 4formation, any flaw in one sheet of mica will be comparatively insi icantfas it will not re'ster with similarL ganws in other layers.4

veferrin'gftoFig. 2,-ths'is the same as Fig.I 1','- except that the Shelli without-constrictionfatits lOWerIend.'-' Y,

:Thus it -will' be 'seen that 'Ilfavefprovided a 'spark'plu'g which-ha's-the desirable qual operated at :high` compression; which'lis: effectively insulated even when operated ata= very high temperature, andwhich moreover, is veryfdurablev anlrug subject'e -to-abr-'lupt temperature changes'.A

'11.3 Als arkfplu fcomprisingfairnetalfshell, e therethrougmqmiea in'= ed at? high temperatures`I and? lwhen i element; and faproteetiveiinsulatingi barrier p05 alii` axial electro e.'

walled -barrier yaroundsaid"electrode andl a` portion* of '.1 sa-id tmica insulation exposed within` 'the""s`l`1ell.4

3.-'A spark-plii comprising a metal shelll an axial electro' e'therethrough", insulating material of-*lgh resistivitywithin said shell around saidr electrode, said electrode havin a terminal projecting beyond said insulating material, a barrier exposed within the interior of the'shell between said insulating material and the electrode: terminal, and in sulating means filling the space Within the metal shellaroun'd the first mentioned in sulating material and the electrode and coinprising'enamel intimately engaging' the invcomprisngf a :metalshell, therethrough; mic'af; in sulationi j' 'around the "electrode withinFthe-L shell-,iam insulating element aroundI said' mica; insulation; insulating material around` saidf side wall of the shell and the electrode by fusion therewith, said enamel having its coefficient of heat expansion near enough to that of the iron to permit differential expansion at operating temperatures without exceeding the elastic ran e.

4. A spark plug comprlsing a metal shell with an interior circumferential ledge, an axial electrode, a washer resting on said ledge around the electrode, a thin walled cup of material of permanent character with respect to heat and abrupt temperature changes lying against said Washer, said cup having a hole in the bottom with the electrode projectin therethrough and insulating material witiin the shell around the electrode and behind said cup as a barrier.

LEONARD KEBLER. 

